As an example of a conventional feed apparatus, a feed apparatus utilized for taper-cutting a workpiece in a wire cutting type electric discharge machining system will be explained in reference to FIGS. 4 and 5.
FIG. 4 is a front view of the conventional feed apparatus and FIG. 5 is a left side view of the feed apparatus.
This conventional feed apparatus 1 for taper-cutting a workpiece comprises a base 12 secured to a lower portion of a Z-slide 11, a U-slide 71 supported by a lower portion of the base 12 through a pair of U-guides 72 for straight movement, and a V-slide slide 81 supported by a lower portion of the U-slide 71 through a pair of V-guides 82 for straight movement. The U-slide 71 is constructed so as to be slidably moved along a U-axis shown by an arrow U in FIG. 4. The V-slide 81 is constructed so as to be slidably moved along a V-axis at a right angle with the U-axis and supports a guide holder 41 which an upper wire guide member 42 is disposed inside. Thus, the feed apparatus 1 moves the upper wire guide member 42 relative to a lower wire guide member along the U-axis and the V-axis, so that a wire electrode 46 extended between both guide members is inclined.
A U-drive unit 73 provided with a U-feed motor 77 and a speed reduction mechanism is attached to the base 12 for rotating a U-feed lead screw 74 which is engaged with a U-nut 75 secured to the U-slide 71. A V-drive unit 83 provided with a V-feed motor 87 and a speed reduction mechanism is attached to the U-slide 71 for rotating a V-feed lead screw 84 which is engaged with a V-nut 85 secured to the V-slide 81.
In addition, as shown in FIG. 5, the base 12 is provided with a recess 13 in its lower portion and the U-slide 71 is provided with a projection 78 in its upper portion. The U-guides 72 are disposed between side edges of the recess 13 and the projection 78. An adjustment bolt 76 is disposed on one side edge of the recess 13 for imparting a preliminary pressure to the U-guides 72. Likewise, as shown in FIG. 4, the U-slide 71 is provided with a recess 79 in its lower portion and the V-slide 81 is provided with a projection 88 in its upper portion. The V-guides 82 are disposed between side edges of the recess 79 and the projection 88 and are imparted with a preliminary pressure by an adjustment bolt 86 disposed on one side edge of the recess 79 of the U-slide 71.
In the conventional feed apparatus having the foregoing construction, since the V-nut 85 is secured to the V-slide 81 and the U-nut 75 is secured to the U-slide 71, the V-slide 81 and the U-slide 71 each require a thickness larger than an external diameter of the nut secured to each slide. Consequently, the thickness of both slides 71 and 81 increases in the Z-axis and whole size and weight of the feed apparatus are rendered larger, thereby causing inaccurate feed movement.
Further, when the adjustment bolt 86 is tightened to impart a preliminary pressure to the V-guides 82, a bending transformation is caused by the preliminary pressure P as shown with a dot line in FIG. 4 in such a manner that lower end portions of both sides of the U-slide 71 are spread, while in an upper portion of the U-slide 71 both sides are pushed up and its central part is pulled back. Likewise, a bending transformation occurs in internal rails 72a of the U-guides 72 secured to the U-slide 71 as shown in FIG. 5 so that the transformation obstructs the U-guides 72 from smoothly guiding the U-slide 71 along the U-axis and causes inaccurate feed movement.